Adequate lubrication of the operating components of a reciprocating piston internal combustion engine is essential since relative motion between unlubricated contacting surfaces will cause excessive wear, overheating, and seizure of the components. The energy loss associated with engine wear and overheating will also result in reduced engine power and efficiency.
A typical reciprocating piston internal combustion engine is equipped with a crankcase oil pan or reservoir for storing the lubricant necessary for normal engine lubrication. An oil pump transports the lubricant to the operating components of the engine. In order to provide sufficient oil pressure at the operating components for adequate lubrication, the oil pump inlet is generally submerged in the reservoir below the surface of the oil, which must be maintained above some minimum level in order to provide sufficient head over the pump inlet and to enable any necessary splash lubrication.
At present, a dipstick is commonly used to determine the level of oil in the crankcase reservoir. The oil level is read by removing the dipstick from the reservoir and comparing the location of the residual oil on the dipstick to lines scribed thereon. The use of a dipstick is inconvenient in a motor vehicle, since the operator must stop the vehicle, and preferably the engine, and dismount to read the dipstick. Nonetheless, dashboard indicators for the level of oil in a motor vehicle oil reservoir are not used. Instead, motor vehicles are equipped with indicators that measure the oil pressure delivered by the oil pump, which is only indicative of inadequate oil in the oil reservoir when there is no longer sufficient oil in the reservoir to keep the pump adequately supplied.